Used by subclasses to paint the radial ink reaction for this control.
The reaction is painted on the given canvas at the given offset. The origin is the center point of the reaction (usually distinct from the point at which the user interacted with the control, which is handled automatically).
Source
void paintRadialReaction(Canvas canvas, Offset offset, Point origin) {
if (!_reaction.isDismissed) {
// TODO(abarth): We should have a different reaction color when position is zero.
Paint reactionPaint = new Paint()..color = activeColor.withAlpha(kRadialReactionAlpha);
Point center = Point.lerp(_downPosition ?? origin, origin, _reaction.value);
double radius = _kRadialReactionRadiusTween.evaluate(_reaction);
canvas.drawCircle(center + offset, radius, reactionPaint);
}
}